Differential sensory block after spinal bupivacaine in volunteers

We performed this study to determine whether differential sensory block to touch, pinprick, and cold after spinal bupivacaine could be used to predict the dermatomal level of block to transcutaneous electrical stimulation (TES) equivalent to surgical stimulation, onset of tourniquet pain, or magnitude of hemodynamic depression. Eight subjects per group were randomized to receive 3.75, 7.5, or 11.25 mg of 0.75% bupivacaine with 8.25% dextrose in a double-blind fashion. Sensory block was assessed with touch, pinprick, cold, TES at T-12, L-2, S-1, and thigh tourniquet pain. Differential extent of sensory block to touch, pinprick, and cold occurred at the time of offset of tolerance to TES (P < 0.03) and at the time of tourniquet pain (P < 0.05). However, the extent of differential sensory block to touch, pinprick, and cold varied up to 10 dermatomes (2 SD) cephalad to block to TES and up to 7 dermatomes (2 SD) cephalad to the thigh tourniquet at the time of intolerable tourniquet pain. Sensory block to cold did not correlate with hemodynamic depression. Differential sensory block occurs after bupivacaine spinal anesthesia, but is a poor predictor for surgical anesthesia, tourniquet pain, and hemodynamic depression.